Process for loading a reactor

ABSTRACT

There is provided a method for loading solid particles into a multi-tube reactor having an upper tube-sheet holding together the upper ends of the multitude of reactor tubes, the method comprising positioning a loading device having a plurality of holes on top of the upper tube-sheet such that the loading device rests on and substantially covers the upper tube-sheet and the holes correspond to the reactor tubes, the loading device comprising a plurality of adjacent polygonal plates, each polygonal plate having from 1 to 30 holes, each hole corresponding to one reactor tube; pouring the particles over the combined polygonal plates covering the tube-sheet; sweeping the particles through the holes in the plates into the respective reactor tubes; removing residual particles and any dust remaining on and between the plates; and removing the loading device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/068,200, filed Mar. 29, 2002, which claims benefit of United Statesdivisional patent application Ser. No. 09/309,924, filed May 11, 1999which is now U.S. Pat. No. 6,409,977. U.S. Pat. No. 6,409,977 claimsbenefit under 35 U.S.C. §119 of Great Britain Application No.98303681.5, filed on May 12, 1998. All of the aforementioned relatedpatent applications are herein incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a method of loading a multi-tube reactor withsolid particles, in particular catalyst particles.

A so-called multi-tube reactor is in essence a shell and -tube exchangercontaining up to several thousands or even tens of thousands ofsubstantially vertical reactor tubes inside its shell, each reactor tubecontaining a fixed bed of catalyst particles and being cooled externallyby a fluid circulating between the tubes in the shell. Multi-tubereactors are used for highly exothermic reactions, such as theepoxidation of ethylene. While the cross-sections of the reactor tubesare relatively small (such as 20-50 nun), their length is great (such as1.5 to 20 m). Inside the reactor shell, the reactor tubes are heldtogether by an upper and a lower tube sheet. Above the tube sheet, thereactor shell forms an upper dome in which maintenance work can beperformed, such as the loading and re-loading of the reactor tubes withcatalyst. In some reactors the upper dome is removable.

The loading or re-loading of the multitude of narrow and elongatedreactor tubes with catalyst, the particles of which are generally notvery much smaller than the inner diameter of the tubes, is difficult andtime-consuming. An even distribution of the catalyst particles insideeach tube and between all tubes is very important but difficult toachieve. During loading it is essential that the number of particlesentering the reactor tube at the same time, multiplied by their greatestdimension, be small enough in relation to the internal diameter of thereactor tube so as to avoid the condition known as “bridging.”“Bridging” occurs when several particles enter and fall down the tubesimultaneously, wedge together part way down the tube and leave a voidspace below them—resulting in unevenly and incompletely loaded tubes.When loading the elongated reactor tubes described above, it is best toensure that the particles enter these tubes one by one. A furtherrequirement, in particular in the ethylene epoxidation reaction whichinvolves gaseous reactants and which is very exothermic, is that a smallupper portion of each reactor tube is kept free of catalyst.

In the past it was conventional to place, in effect, a funnel at theupper end of each reactor tube and pour the particles into theindividual tubes. Such a procedure is unacceptable today because of thelarge number of tubes which have to be filled.

U.S. Pat. No. 3,223,490, issued 14 Dec. 1965, discloses a reactor tubeloader which comprises (a) a perforated plate which rests on the reactortubes, the perforations corresponding to the pattern and spacing of thereactor tubes; and (b) fill tubes, one for each reactor tube, which nestin the perforated plate and extend into the corresponding reactor tubes.In operation, catalyst 1S dumped onto the perforated plate and the plateis shaken by a vibrating mechanism, causing the catalyst particles topass one by one through the fill tubes and into the reactor tubes. Thesame publication adds that the fill tubes may be made of such lengththat when they are loaded to their top with catalyst and then removedfrom the reactor tubes, their content fills the reactor tubes up to apredetermined point below the top thereof.

GB-B-2186209, issued 1 Feb. 1989, also discloses a reactor tube fillingdevice consisting of a plate resting on the reactor tubes and fill tubesnesting in the plate and extending into the corresponding reactor tubes.The differences with the first document are that the fill tubes arefirmly connected to the plate and that a vibrating mechanism is notmentioned. The function of the device according to this document is toensure that all reactor tubes are filled to a fixed level below theirtop. The phenomenon of bridging is not mentioned.

The above catalyst loading devices have serious disadvantages. Inparticular, they are inflexible in that a plate and its associatedfilling tubes can only be used in a multi-tube reactor of the same sizeand shape, having the same number, pattern, spacing and diameter ofreactor tubes. They are also big, heavy and cumbersome to transport andto introduce into the upper reactor dome.

It is an object of the present invention to provide a much simpler andmore flexible loading system for multi-tube reactors. This object J.Sachieved by using a multitude of discrete polygonal plates as definedbelow, to close-pack the upper tube sheet in a two-dimensional array,i.e. to entirely cover any shape and size of upper tube sheet, in thesame way as tiles are used to cover a floor. Together, the polygonalplates form an exceedingly simple and flexible multi-tube loadingdevice.

SUMMARY OF THE INVENTION

The present invention provides a loading device for distributing solidparticles into a multi-tube reactor in which the reactor tubes aresubstantially vertical and held together by an upper and a lower tubesheet, the loading device comprising a plurality of adjacent polygonal,i.e. triangular, quadrangular or hexagonal, plates, each polygonal platehaving from 1 to 30 holes, each hole corresponding to one reactor tube,each hole having an diameter not greater than 95% of the inner diameterof the reactor tube and not smaller than 1.1 times the greatestdimension of a single particle to be loaded, the polygonal plates alsocomprising fixing means for holding the holes in correspondence with therespective reactor tubes.

The present invention also provides a method for loading solid particlesinto a multi-tube reactor, the reactor tubes having an inner diameter ofat least 2 times the diameter of a single particle to be loaded therein,the reactor having an upper tube-sheet holding together the upper endsof the multitude of reactor tubes, the method comprising the followingsteps:

-   -   a) positioning a loading device on top of the upper tube-sheet,        such that the combined polygonal plates substantially cover the        upper tube-sheet and their holes correspond to the reactor        tubes, wherein the loading device comprises a plurality of        adjacent polygonal plates, each polygonal plate having from 1 to        30 holes, each hole corresponding to one reactor tube, each hole        having an diameter not greater than 95% of the inner diameter of        the corresponding reactor tube and not smaller than 1.1 times        the greatest dimension of a single particle to be loaded into        said reactor tube, the polygonal plates also comprising fixing        means for holding the holes in correspondence with the        respective reactor tubes;    -   b) pouring the particles over the combined polygonal plates        covering the tube-sheet;    -   c) sweeping the particles through the holes in the plates into        the respective reactor tubes, whereby the particles fill the        reactor tubes in a uniform manner and bridging is avoided;    -   d) removing residual particles and any dust remaining on and        between the rims; and    -   e) removing the loading device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a top view of part of the loading device ofthe present invention in its embodiment according to the Example; and

FIG. 2 shows a section of FIG. 1 along the line II-II.

DETAILED DESCRIPTION OF THE INVENTION

Each polygonal plate of the loading device according to the inventionrests on the upper sheet of the multi-tube reactor with its hole orholes, the number of which is up to 30, corresponding to respective topsof reactor tubes and being kept in place by fixing means.

The inner diameter of a hole in the polygonal plate is chosen inrelation to the particles to be handled, so as to ensure that bridgingis avoided. In order to avoid bridging, the number of particles enteringa reactor tube at any moment, multiplied by their greatest dimension,should be substantially less than the inner diameter of the reactortube. In practice, the particles enter the reactor tube one by one.Broadly, the inner diameter of a hole is not greater than 95% of theinner diameter of the reactor tube and not smaller than 1.1 times thegreatest dimension of the particles to be loaded, but more suitably itis from 1.2-2. a times the greatest dimension of these particles.

The fixing means for holding the hole or holes in correspondence withthe respective reactor tube or tubes can in principle be chosen to beindividual to each hole or common to the entire device. There are manymore or less simple possibilities to effect this means. Of course, thesimpler the fixing means the easier the operation will be and for thatreason screws and bolts are not preferred. Suitably, the fixing means isan insert extending from the edge of the hole into the top of thereactor tube and having a length of from 0.5 cm to 1.5 meter. The formof such an insert can be anything from at least one spike to a completepipe, including intermediate forms such as a half-pipe.

Preferably, the fixing means is an insert in the form of a pipe orhalf-pipe having the same or a smaller inner diameter than the hole inthe plate and extending from its edge into the reactor tube. Of coursethe longer this insert is the slower will be the filling and the greaterthe void remaining in the upper part of the tube when the insert isretracted. Preferably the length of the insert is from 2 to 100 cm, morepreferably from 2 to 50 cm. Most preferably the length of the insert isfrom 1.1-1.5 times the depth of the upper part of the reactor tubewhich, when loaded, is to be kept free of particles.

When the insert is long, it is advantageously made of flexible materialor in extensible form.

When the insert is in the form of a pipe, tapered in downward directionand/or provided longitudinal compression slot.

The polygonal plate of the loading device according to the invention hasa triangular, quadrangular or hexagonal shape. Its dimensions are suchas to ensure that when in place it will not interfere with neighbouringreactor tube openings. Preferably the dimensions of the polygonal plateare such that when in place the distance between neighbouring upper rimsis smaller than the greatest dimension of the particles to be loaded,thus ensuring that no particles will be captured between plates. On theother hand a small inter-plate space is convenient for ease of handlingand for accommodating the dust which inevitably develops during theloading work, thus avoiding that the dust is swept into the reactorpipes. The triangular, quadrangular or hexagonal shape of the polygonalplate ensures that the inter-plate spaces will always be uniform.

In profile, the polygonal plate may be undercut in its downward surface,so as to allow even more space for accommodating the dust. Alternativelythe insert extending from the polygonal plate into the reactor tube canbe made to carry a shoulder which will also allow space between thepolygonal plate and the upper tube sheet for accommodating dust. Thelength of the shoulder can suitably be about 1 em. For the same purposeof accommodating dust, the polygonal plate can be perforated with slitsor small holes. The polygonal plate may also taper in its upward surfacetowards the hole or holes, in order to facilitate the particles' fallinginto the reactor tube.

The simplest and most preferred embodiment of the loading deviceaccording to the invention is when it consists of a multitude ofpolygonal plates, each having a single hole to correspond with onereactor tube, and fixing means as described above. In that case thepreferred shape of the polygonal plate is hexagonal, square, rhomboid ordiamond-shaped. When a polygonal plate carrying multiple holes is used,its shape can most conveniently be rectangular, e.g. in the form of astrip carrying one or more rows of inserts. Such a strip can be madeflexible, for greater ease of transport and handling.

The loading device according to the invention can be made of anyconvenient material, preferably one that is robust enough to allow forreusing the loading device. Examples are metals such as stainless steeland aluminium, and polymers such as polypropylene and polyvinylchloride.

In operating the loading device according to the invention, thepolygonal plates are first placed in position over the upper tube sheetsuch that all reactor tubes correspond at their upper ends to holes inthe plates and the combined plates substantially cover the tube sheet inpart or entirely. Then the particles are poured over the surface of thecombined plates. Next, the particles are forced through the holes andinto the reactor tubes by sweeping. The sweeping can be done manually,e.g. with simple brooms. Alternatively, a sweeping mechanism can beused, such as a mechanically operated central axis from which a rotatingarm extends which carries a sweeping element, preferably along itsentire length. However, the actual manner of sweeping is not essentialto operating the invention because the loading device itself ensures aquick and relatively convenient uniform loading of all reactor tubes. Asindicated above, when the polygonal plates carry inserts the length andcalibre of the insert, in relation to the calibre of the reactor tube,will determine the depth of the upper end of the reactor tube which willremain empty after the insert is removed.

The invention will be further illustrated by the following Example andFigures.

EXAMPLE

Four chemical reactors, each comprising about 3000 vertical reactorpipes, each reactor pipe having an outer diameter of 45.2 mm, an innerdiameter of 39.2 mm, and a length of 12.8 m, the distance betweenneighbouring pipes being 63 mm, were loaded with catalyst particleshaving the basic shape of a cylinder with a diameter of 8 mm and alength of 8 mm.

Loading devices were used, each of which was made of polypropylene andconsisted of a multitude of hexagonal plates. Each hexagonal plate was59.0 mm across the minor axis and 69.0 mm across the major axis, with athickness of 5.0 mm, and had a single central hole of 23.8 mm ( 15/16inches) in diameter, and a slotted insert extending at a right anglefrom the edge of the hole. Each insert was in the form of a tapered pipe30.0 mm In length, 39.0 mm outside diameter, ‘35.0 mm inside diametertapering to 38.0 mm outside diameter and 35.0 mm inside diameter, andhad a compression slot 3 mm wide extending the full length of 30 mm,allowing a tight fit.

In operation each hexagonal plate device was positioned manually withits insert extending into one of the reactor pipes to be loaded. Thereactor pipes which did not require loading were plugged with a plasticcap. The configuration ensured that the whole tubesheet was effectivelycovered excepting regular gaps of 3 mm width left between neighbouringloading devices.

The reactor was covered in strips of rubber sheeting, each about 80 cmwide and of sufficient length to extend from one side of the reactor tothe other, the maximum length being 450 cm, to prevent any foreignobjects falling through an orifice into the reactor pipe. The reactorwas loaded in sections, with each section being exposed by the removalof a strip of rubber sheeting. The loading was performed methodically inthat the loading of one section was completed before the loading of asubsequent section was started.

The catalyst was tipped from drums each of which contained about 200litres of catalyst into a loading hopper.

The outlet of the hopper had a tube of canvas, of 203 nun diameter,through which the catalyst poured. The tube of canvas had a dust removaldevice attached to minimise the dust reaching the loading devices. Thecatalyst was poured on to the first section and manoeuvred over theorifices by hand. As the catalyst particles moved attrition caused somedust generation. The gap between the loading devices served as a dustcatchment area.

The gap was sufficiently small as not to allow any whole catalystparticles to enter, but allow small chips and broken pieces of catalyst.

The hexagonal plates were removed manually. In order to avoid damage bypulling on the holes of the hexagonal plates, a Y-shaped manual removaltool was designed and used to operate on the hexagonal plate edges.

After removal of the loading device, the catalyst level in each reactortube dropped below the level of the tubesheet. Vacuum was then used tofurther evacuate catalyst particles from the top of each reactor pipe toa level of about 305 nun (12 inches) below the tube sheet.

A dP-check (pressure drop over the reactor pipes) was performed bypassing a constant flow of dry oil-free air through each tube anddetermining the pressure drop generated over a restricted orifice plate(ROP). Typical for a good catalyst distribution is a dP in each tube ofwithin ±2.5% of the mean. The dP-check showed that an even distributionof catalyst particles inside each reactor pipe as well as amongindividual pipes has been achieved and that no pipes required unloadingand refilling.

Referring to FIGS. 1 and 2, during normal operation, the loading device1 is arranged in a substantially vertical multi-tube reactor (not shown)which comprises a plurality of reactor tubes 3 which are held togetherby an upper tube sheet 5 and a lower tube sheet (not shown). The loadingdevice 1 is arranged to cover at least part of the upper tube sheet 5.

The loading device 1 comprises a plurality of adjacent polygonal plates8. In the embodiment shown, the polygonal plates 8 are hexagonal, eachhaving a minor axis 9 and a major axis 10 and each having a single hole11.

Each hole 11 corresponds to one reactor tube 3, that is to say each holeis arranged above the corresponding reactor tube 3. To hold the hole 11in correspondence with the respective reactor tube, each hexagonal plate8 further comprises fixing means for holding the hole 11. In theembodiment as shown in FIG. 2, the fixing means is a tapered pipe 15provided with a compression slot 16.

Suitably the distance 19 between neighbouring hexagonal plates 8 issmaller than the largest dimension of a single particle (not shown) tobe loaded.

1. A loading device for loading particles in a multi-tube reactor,comprising: a discrete plate having a shape that provides a spacingbetween adjacent plates positioned on the multi-tube reactor to collectdust and partial particles, wherein a single aperture through the platecorresponds to and aligns with a single respective reactor tube withinthe multi-tube reactor.
 2. The loading device of claim 1, wherein theshape enables placement of the plate on the multi-tube reactor proximatethe single respective reactor tube without interfering with neighboringreactor tube openings.
 3. The loading device of claim 1, furthercomprising an insert extending from the discrete plate, the insertconfigured to at least partially extend into the respective reactortube.
 4. The loading device of claim 1, further comprising a tubularinsert extending from the discrete plate, the tubular insert configuredto at least partially extend into the respective reactor tube.
 5. Theloading device of claim 1, wherein the discrete plate is made of apolymer.
 6. The loading device of claim 1, wherein the discrete plate ismade of a polypropylene.
 7. The loading device of claim 1, wherein thediscrete plate is made of a polyvinyl chloride.
 8. The loading device ofclaim 1, wherein the spacing has a width less than the smallestdimension of a single whole particle.
 9. The loading device of claim 1,further comprising a tubular insert extending from the discrete platearound the single aperture, the tubular insert configured to extend intothe respective reactor tube a depth of from 1.1 to 1.5 times apredetermined depth of the respective reactor tube that is to be keptfree from particles when loaded.
 10. A loading device for loadingparticles in a multi-tube reactor, comprising: a discrete plate having ashape that provides a spacing between adjacent plates positioned on themulti-tube reactor to collect dust and partial particles, the spacinghaving a width less than the smallest dimension of a single wholeparticle, wherein the plate has at least one aperture that correspondsto and aligns with at least one respective reactor tube within themulti-tube reactor.
 11. The loading device of claim 10, furthercomprising at least one insert extending from the at least one aperture,the at least one insert configured to at least partially extend into theat least one respective reactor tube.
 12. The loading device of claim10, wherein the discrete plate is made of a polymer.
 13. A method forloading solid particles into a multi-tube reactor, comprising:positioning a plurality of discrete plates on top of an upper tube-sheetof the multi-tube reactor, whereby the plates substantially cover atleast a portion of the upper tube-sheet and each plate has a shape thatprovides a spacing between adjacent plates having a width for collectingdust and partial particles; pouring the particles over at least aportion of the plates covering the tube-sheet and into apertures throughthe plates; and removing any dust remaining in the spacing betweenadjacent plates.
 14. The method of claim 13, wherein the shape of eachplate enables the positioning of the plurality of discrete plates on themulti-tube reactor such that each of the plurality of discrete platesare proximate a single respective reactor tube without interfering withneighboring reactor tube openings.
 15. The method of claim 13, whereinthe positioning the plurality of discrete plates comprises insertingfixing means of the plates into a top of reactor tubes of the multi-tubereactor to provide for alignment of the apertures in the plates withcorresponding reactor tubes.
 16. The method of claim 13, wherein thepositioning the plurality of discrete plates comprises disposing insertscoupled to the plates into a top of reactor tubes of the multi-tubereactor to provide for alignment of the apertures in the plates withcorresponding reactor tubes.
 17. The method of claim 13, wherein thespacing has a width less than the smallest dimension of a single wholeparticle.
 18. The method of claim 13, wherein each of the plurality ofdiscrete plates have a single aperture corresponding to and aligningwith a single respective reactor tube within the multi-tube reactor. 19.The method of claim 13, wherein the plurality of discrete plates aremade of a polymer.
 20. The method of claim 13, further comprisingremoving the plurality of discrete plates.